This invention relates to a tape driving mechanism for a tape recorder, in which a torsion coil spring for urging a pinch roller against a capstan shaft is provided on a portion of a pinch roller holder.
In the usual tape recorder, a magnetic tape is pinched between a capstan shaft and a pinch roller and is driven as the capstan shaft rotates, while a magnetic head is held in contact with the tape during recording or reproduction.
The pinch roller must be urged against the capstan shaft to feed the magnetic tape. Usually, a torsion coil spring is used to urge the pinch roller against the capstan shaft.
Usually, the torsion coil spring is mounted as shown in FIG. 1. A pin 102 is provided on a base plate 101 of the recorder and projects upright. A pinch roller holder 103 is rotatably mounted on one end on the pin 102. A pinch roller 104 is rotatably supported by the pinch roller holder 103 at an end portion thereof opposite the pin 102. A torsion coil spring 105 is mounted on the pin 102, with its ends engaged with portions of the pinch roller holder 103. When one end portion of the torsion coil spring 105 is urged in the direction of the arrow in FIG. 2, the pinch roller holder 103 is rotated. When the end portion of the spring 105 is a little further urged after the pinch roller 104 has been brought into contact with the capstan shaft 106, it is slightly deformed as shown in FIG. 3. In this state, a restoring force corresponding to the contact force between the capstan shaft 106 and pinch roller 104 is stored in the spring 105.
In the above construction, the torsion coil spring 105 is mounted on the pin 102 and held in forced contact therewith at point P as shown in FIG. 4. Therefore, a contact resistance is produced between the spring 105 and pin 102 when the pinch roller holder 103 is rotated. This reduces the contact force between the capstan shaft 106 and pinch roller 104. In addition, the pin 102 and spring 105 are liable to be damaged due to local friction between the pin 102 and spring 105. Further, the spring 105 must be mounted on the pin 102 at the same time the pinch roller holder 103 is mounted on the pin 102. Considerable skill is therefore required for mounting these components.
In order to solve the above problems, a tape driving mechanism shown in FIG. 5 has been proposed. In this mechanism a pinch roller holder 103 has a sleeve 107 coaxial with the axis of its rotation. This sleeve 107 is fitted on a pin 102. A torsion coil spring 105 is mounted on the outer periphery of the sleeve 107 so that it is not in direct contact with the pin 102.
With this construction, since the spring 105 and pin 102 do not contact, the pinch roller 104 can be strongly urged against the capstan shaft 106. For the same reason, the pin 102 and spring 105 are not damaged. Further, the pinch roller holder 103 and spring 105 may be easily mounted by first putting the sleeve 107 on the pinch roller holder 103, then fitting the spring 105 on the sleeve 107 and finally fitting this assembly on the pin 102.
The construction of FIG. 5, however, uses the sleeve 107 as an additional part, so that it is more expensive than the construction of FIGS. 1 to 4.